Photoelectric amplifier



Patented Feb. 21, 1939 PATENT OFFICE,

PHOTOELEOTRIC AMPLIFIER August Karolus, Leipzig, Germany, assignor to Radio Corporation of America, a corporation of Delaware Application January 3, 1935, Serial No. 245 In Germany January 3, 1934 1 Claim.

The object of this invention is a construction element comprising a photo-electric tube, coupling resistance, and amplifier tube adapted to electro-optic work, especially television. This element which is designed to constitute a selfcontained unit of suitable dimensions shall hereinafter be designated as a photo-electric amplifier; it may be assembled in groups of any desired size, so as to result in, for instance, a transit) mitter panel or board for the scanning of a picture transmission equipment. Elements of this kind and provided in convenient numbers may moreover be co-ordinated to an optical distributor, for the purpose of serving as controlled relays for light amplification and storing in highgrade television work, especially to obtain larger and brighter picture surfaces or areas at the receiving or re-creating end.

The invention consists of the following constructionally preferable electrical arrangement and assembly: photoelectric tube, grid resistance and amplifier tube of reduced size or cross-section are connected in series at close proximity to one another, and are built together with short 55 low-capacity leads, so that, in the presence of the smallest possible cross-sectional size of this construction or cell element, there results a time constant in the assembly that will be adequately low for all practical purposes, while by the insertion of an amplifier tube in the combination the output resistance for transmission lines or the luminous photoelectric tubes of the receiver board or panel will be sufi'iciently low. In view of the combination of a great number of such elements 5 to result in a cellular board in accordance with suggestions well known from the earlier art, a further advantage of the embodiment of this invention consists in that the adaptation or balancing of the elements to a definite slope (mil- 0 liamps per lumen) prior to their use is feasible individually in a very simple manner, and that subsequently when in actual operation and use, substitution in the form of closed units is made particularly easy and convenient. Moreover, by

3 the combination and assembly of the said parts inside a metallically screening or shielding tubular casing there is insured a chance for obtaining perfect freedom from disturbances or interference and the protection of the inside insulation from moisture.

Fig. 1 shows schematically the cross-section of an embodiment of the basic idea of the invention. Inside a metallic sheath or casing I is arranged at the top end the photo-electric tube 2 l comprising the light-responsive coat 3 and the anode 4. The conducting lead of 4 is in direct connection with the body I, for instance, in that a spring riveted or soldered thereto comes to boards suitably 100 to 200 megohm) which is inl0 troduced laterally with proper insulation, and which is held, e. g., by the agency of a contact spring at 6 to which the external source of potential is connected and which is insulated from the metallic housing by bushing l5. If the latl5 eral projection of 6 is considered a nuisance in compact construction and assembly of the elements, the mounting for 5 may be provided at some other place of the tube. 8 designates the amplifier tube whose grid is brought out at 1 20 with proper insulation in order that the grid capacity may be rendered as low as feasible. 9 designates the leads of the other electrodes of 8; l0 and II designate the felt rings or washers provided for fixing the tubes 2 and 8; I2 is an 5 insulating closure plate which may be provided with plug prongs in order that the whole element may be fitted into a suitable socket for the simultaneous electrical connection. l3 and I4 designate insulating closure plates for supporting the resistance 5 and the fiat conducting strip l6 which connects the coating of the photoelectric tube 3, the resistance 5 and the control electrode of the vacuum tube 8. For building up a mosaic or cell board comprising, e. g., 10,000 elements, the diameter of tube I would be made 10 or at most 20 mm.

' Fig. 2 illustrates the easily understandable connection of the difierent parts of the cell element. The grid resistance 5 being adapted to be readily 40 fitted in and to be removed laterally by means of the spring clip H, by variation of its ohmic value allows of a subsequent change in the overall sensitivity so that disparities in the photoelectric tubes or in the characteristics of the amplifier tubes may subsequently be compensated.

If in a way as hereinbefore disclosed photoelectric amplifier elements are assembled to result in mosaics of cellular boards or panels, it will be found that when a critical number of cells has been reached it will be impossible for reasons of insuflicient space to accommodate all of them in a single plane. In this instance, the light-ray pencil is split into subdivisional pencils by the agency of mirrors disposed in the projection path 5 and positioned at appropriate angles in relation to one another, said partial pencils being deviated towards different directions where they are caused to impinge upon convenient groups of cells which correspond to portions of the picture.

In nearly all cases will it be found advantageous to operate the amplifier tube of the described cell element at the anode end directly on A. C. or else to make the light of the original picture reaching the photoelectric tube intermittent by means of periodic diaphragming or eclipsing. If for reasons of adaptation the plate alternating potential is to be transformed or stepped down in such instances a transformer will be required therefor. The assembly of these latter, for electrical reasons, is preferably disposed immediately below the common supporter plate or base of the cell elements, whereby the whole is at the same time combined into a single assembly. If the cross-section of the transformer should happen to be larger than that of the cell element, then the transformers may be disposed staggered in several layers or tiers in order that all of them may be accommodated inside the surface area of the cell or mosaic board.

If photo-electric amplifier elements according to this invention are assembled in such a number that for each screen point of the picture field there is provided an independent element coordinated thereto, 1. e., if all points or elementary areas of the picture screen are simultaneously transmitted, then the inertia of the aggregate arrangement must be limited to such an extent that from 20 to 30 changes in luminosity each second will still be renderable without any appreciable loss in the modulation percentage. This is successful even with thin-wired glow-lamps acting as luminous cells mounted in the picture recreating panel. Experience has shown that when the amplifier tube whose grid is controlled by the photoelectric tube D. C. voltage is operated at the plate end with A. C. it is wholly permissible and quite sufficient from a technical viewpoint to use supply lines of 50 cycles per second. It will be understood, of course, that the frequency could be chosen even higher than that. However, an upper limit is imposed, if the frequency is not unduly high, by the capacitive leakance of the transmission channel. The advantage of A. C. operation at the anode end and the avoidance of D. 0. supply consists in that, by means of transformation, it will always be feasible to attain extensive adaptation, and that both rectifiers as well as smoothing means required in D. C. operation may be eliminated.

I claim:

A unitary photoelectric amplifier comprising a photoelectric tube having an anode and a cathode mounted in an envelope, a resistance external to said envelope and connected to one electrode of said tube, a source of potential across said photoelectric tube and resistance in series, a vacuum tube including an anode, a cathode and a control electrode mounted in a separate envelope, said control electrode connected to said resistance, the potential of the control electrode being adapted to vary in accordance with the variations in potential developed across the resistance as a result of the variation in thermionic current flow in said photoelectric tube, an output circuit for said vacuum tube, and a metallic housing which surrounds, shields and supports said photoelectric tube, resistance and vacuum tube, said housing acting as an electrical conductor from said source of potential to the other electrode of said photoelectric tube, said photoelectric tube, resistance and vacuum tube each being readily and individually replaceable in said housing.

AUGUST KAROLUS. 

